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fuzz/clock.c

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+/*
+ * Copyright (c) 2021 Yubico AB. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <stdint.h>
+#include <time.h>
+
+#include "mutator_aux.h"
+
+/*
+ * A pseudo-random monotonic clock with a probabilistic discontinuity to
+ * the end of time (as measured by struct timespec).
+ */
+
+extern int prng_up;
+extern int __wrap_clock_gettime(clockid_t, struct timespec *);
+extern int __real_clock_gettime(clockid_t, struct timespec *);
+extern int __wrap_usleep(unsigned int);
+static TLS struct timespec fuzz_clock;
+
+static void
+tick(unsigned int usec)
+{
+	long long drift;
+
+	/*
+	 * Simulate a jump to the end of time with 0.125% probability.
+	 * This condition should be gracefully handled by callers of
+	 * clock_gettime().
+	 */
+	if (uniform_random(800) < 1) {
+		fuzz_clock.tv_sec = LLONG_MAX;
+		fuzz_clock.tv_nsec = LONG_MAX;
+		return;
+	}
+
+	drift = usec * 1000LL + (long long)uniform_random(10000000); /* 10ms */
+	if (LLONG_MAX - drift < (long long)fuzz_clock.tv_nsec) {
+		fuzz_clock_reset(); /* Not much we can do here. */
+	} else if (drift + (long long)fuzz_clock.tv_nsec < 1000000000) {
+		fuzz_clock.tv_nsec += (long)(drift);
+	} else {
+		fuzz_clock.tv_sec  += (long)(drift / 1000000000);
+		fuzz_clock.tv_nsec += (long)(drift % 1000000000);
+	}
+}
+
+int
+__wrap_clock_gettime(clockid_t clk_id, struct timespec *tp)
+{
+	if (!prng_up || clk_id != CLOCK_MONOTONIC)
+		return __real_clock_gettime(clk_id, tp);
+	if (uniform_random(400) < 1)
+		return -1;
+
+	tick(0);
+	*tp = fuzz_clock;
+
+	return 0;
+}
+
+int
+__wrap_usleep(unsigned int usec)
+{
+	if (uniform_random(400) < 1)
+		return -1;
+
+	tick(usec);
+
+	return 0;
+}
+
+void
+fuzz_clock_reset(void)
+{
+	memset(&fuzz_clock, 0, sizeof(fuzz_clock));
+}